1. Technical Field
The disclosure relates to a charge pump circuit and relevant method thereof, and more particularly to a charge pump circuit with adjustable output voltage and a power-supply method for dynamically adjusting output voltage.
2. Related Art
A charge pump circuit is usually applied to the driving circuit in every type of electrical product. The charge pump circuit processes voltage conversion using the charging and discharging characteristics of the capacitors to provide desired output voltage.
FIG. 1 is an explanatory diagram of a charge pump circuit. Referring to FIG. 1, a charge pump circuit 10 includes an electric charge pump unit 12, a flying capacitor Cf, a first storage capacitor Cp1 and a second storage capacitor Cp2.
The electric charge pump unit 12 charges and discharges the flying capacitor Cf, the first storage capacitor Cp1 and the second storage capacitor Cp2 according to a charge pump clock CKp, so as to convert an inputted source voltage VDD into a desired positive output voltage VPP and a negative output voltage VEE. The difference between the positive output voltage VPP and the negative output voltage VEE is usually several times (such as two times) the source voltage VDD, and the conversion is processed in constant and single-mode.
Regarding to the power supply planning for the whole coding/decoding chip (CODEC IC), aside from driving devices of speakers that required higher output Watts, driving devices of headphones consume much power as well. In many designs for the driving devices of the headphones, the charge pump circuits are used to generate a steady negative voltage (−VDD) to supply an amplifier circuit. Although expensive coupling capacitors in the driving end of the headphone is saved, there is still the problem of a high power-consumption problem. In these designs, the positive power end of the amplifier circuit is usually connected to a voltage source of the system (providing the source voltage VDD), while the negative power end is coupled to the charge pump circuit. Therefore, all the static power consumption of the amplifier circuit flows from the positive power end (VDD) to the negative power end (−VDD), rather than to the ground end of the system. The current flowing to the negative power end is counteracted through the charge pump circuit consuming the same current, such that the whole circuit framework must use twice as much power. Furthermore, when considering the power conversion efficiency of the charge pump circuit itself, the total power consumption will further increase.
In addition, when the amplifier drives a device, such as a headphone, regardless of the amplitude of the output signal, the charge pump circuit still generates the negative voltage (−VDD) with a fixed value. Since the audio signal amplitude to headphone is usually much less than the VDD value, it would result in poor efficiency of the entire circuit framework during the low output power operation.